1. Field of the Invention
This invention relates generally to the field of reactive composites comprising nanoparticles. More particularly, it relates to fluorinated acrylic reactive nanocomposites and methods of making and using the same.
2. Description of the Related Art
Reactive nanocomposites combine the high reaction rates of molecular explosives and materials with the high energy density of composite materials. A reactive nanoparticle composite (nanocomposite) typically comprises a fuel such as reactive metal nanoparticles incorporated into a polymer matrix, which acts as an oxidizer. Reactive metal nanoparticles typically include Al, B, Mg, Si, Zr, Hf, Fe, and Ti or alloys or mixtures thereof. To achieve the enhanced reaction rates and mechanical properties typically observed for reactive nanocomposites, the metal nanoparticle should be distributed evenly throughout the polymer matrix, and a variety of methods exist to combine the metal nanoparticles and the polymer matrix. One common method includes powder compaction, which involves sonochemical mixing of the metal nanoparticles with the polymer powder(s) in a solvent, followed by evaporation of the solvent and mechanical compression of the mixed powders into pellet form. Other common methods include melt blending and solution mixing.
However, these methods share a number of limitations and drawbacks. The resulting nanocomposites generally possess minimal chemical and/or physical interaction between the individual component particles (polymer-metal and polymer-polymer), and the metal nanoparticles are often unevenly distributed throughout the polymer matrix. Both of these problems may lead to a nanocomposite that fails to achieve adequate mechanical properties for many practical applications. To obtain better bonding between the individual components, a binder material may be added, but due to the high specific surface area of nanoparticles, a significant amount of binder is often required. The binder may then interfere with the material properties and performance of the composite material. Additional processing steps such as sintering or extrusion may also be performed. However, sintering is often performed at elevated temperatures that are near the temperature required to initiate pre-ignition reactions in the nanocomposite. In addition, processing of some polymers by extrusion requires additional chemicals and/or solvents that may affect the mechanical properties of the reactive nanocomposite. Various in-situ polymerization techniques have been developed to improve distribution of the metal nanoparticles in the polymer matrix and to improve interaction between the nanoparticle and the polymer.
Polytetrafluoroethylene (PTFE) is one of the most common fluorinated polymers used in nano-metal/polymer nanocomposite reactive systems. PTFE has a fully fluorinated carbon backbone, resulting in a fluorine density of 75% by weight, higher than any other fluorinated polymer system. Additionally, PTFE is available in both micron- and nano-scale powders that are amenable to mixing with many metal nanoparticles. However, PTFE is generally not compatible with in-situ polymerization techniques. Suspension or dispersion polymerizations are commonly used to prepare high quality PTFE, but these approaches require the use of both an aqueous layer and elevated temperatures, which limits the polymer's compatibility with many reactive metals like aluminum that react with water, especially at elevated temperatures. In addition, processing of PTFE by extrusion requires the addition of other chemicals and/or solvents or modification of the polymer backbone to yield a co-polymer. This step adds considerable cost to the material and makes it less attractive to the end user.